mm/vmscan: fix highidx argument type

mm/vmscan: fix highidx argument type

for_each_zone_zonelist_nodemask wants an enum zone_type argument, but is
passed gfp_t:

  mm/vmscan.c:2658:9:    expected int enum zone_type [signed] highest_zoneidx
  mm/vmscan.c:2658:9:    got restricted gfp_t [usertype] gfp_mask
  mm/vmscan.c:2658:9: warning: incorrect type in argument 2 (different base types)
  mm/vmscan.c:2658:9:    expected int enum zone_type [signed] highest_zoneidx
  mm/vmscan.c:2658:9:    got restricted gfp_t [usertype] gfp_mask

convert argument to the correct type.

Signed-off-by: Michael S. Tsirkin <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Suleiman Souhlal <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>